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osteosynthesis of ACB fractures is not yet standard therapy based on recommendations in current textbooks (Ruggles, 2019; McIlwraith, 2020; Ross, 2011). However, de Preux and co-authors have demonstrated
the advantages of surgical stabilisation of ACB fractures. Healing was rapid and without complications, and the horse returned to competition. Fixation was aided by precise localisation of the implants using CAOS. Christoph Koch and colleagues have gained a great deal of experience with this technique in recent years. Computer-assisted orthopaedic surgery was originally used in Zurich by Auer et al. in 2005 and 2006 (Andritzky et al., 2005; Gygax et al., 2006). At that time, the method required the placement of markers in the bone to facilitate reliable orientation of the bones, the instruments and the implants using the infrared camera. Nevertheless, small deviations persisted, which is why the technique did not become established. Koch and colleagues developed an alternative to using pins in the bones by fixing the limb in a hard shell, which prevented movement and acted as a reference for the infrared camera. This improved technique allows increased surgical precision and has been used to successfully treat various orthopaedic problems in horses (De Preux et al., 2020a; De Preux et al., 2020b). De Preux et al. (2022) used CAOS to insert two lag screws, a 4.5-mm and a 3.5-mm cortical screw, into the ACB of their patient. The 4.5-mm cortical screws likely provided better stability than 3.5-mm cortical screws because the latter are much less stable for fracture treatment in horses. The core diameter of 3.5-mm cortical screws is small at 2.5 mm, which provides limited bending stiffness, and markedly little compression is achieved because the screw head is small. In contrast, the 4.5-mm cortical screw provides excellent compression of various fractures. The use of CAOS allowed precise placement of the lag screws into the ACB, leading to a good outcome. We believe that surgical fixation will be the preferred
option for the treatment of ACB fractures in the future. Fixation can be done using lag screws, as described by de Preux et al. (2022), or with plates. The application of plates is somewhat easier because they can be applied laterally, which provides ample space for the screws. Based on our experience with plate fixation, this approach would likely eliminate the need for CAOS provided that the surgeon has an in-depth knowledge of the anatomy. The extensor carpi ulnaris muscle has two distal tendons; one inserts directly onto the ACB, while the other runs distally in a tendon groove lateral to the ACB (Figs 3 and 4). Often, the vertical fracture runs close to this tendon groove, which makes the application of a plate difficult. This requires a reconstruction plate that can be moulded to accurately fit the bone and screws that allow for a certain degree of angulation. These plates are mainly used in human medicine and are only now being introduced into veterinary medicine. However, the use of human implants is expected to increase in veterinary surgery. This article illustrates the evolution of fracture treatment in
horses. Improved imaging techniques may now facilitate surgical repair of fractures that were difficult or impossible to treat in the past. The combination of improved imaging methods with superior implants ushers in an array of future possibilities. Similar developments have been observed in other equine bones. For example, most coffin bone fractures
Fig 3: Illustration of the lateral aspect of the accessory carpal bone with the two tendons of the ulnaris lateralis muscle. Ca, accessory carpal bone; S, insertion of one of the tendon of the ulnaris lateralis muscle; L, second tendon of the ulnaris lateralis muscle.
Fig 4: Illustration showing the carpus in cross section. The blue arrow indicates the tendon of the ulnaris lateralis muscle.
are now successfully repaired with screws, thereby substantially reducing the risk of nonunion.
Acknowledgement
Open Access Funding provided by Universitat Zurich. [Correction added on 12 April 2022, after first online publication: Consortium of Swiss Academic Libraries (CSAL) funding statement has been added.]
© 2022 The Authors. Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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